In recent years, fine-line circuitry is demanded in a printed circuit board as the density of semiconductor integrated circuits is increased. A common method of producing fine-line circuitry is the modified semi-additive process (MSAP) of which circuits are formed on an ultrathin copper layer, followed by removing the ultrathin copper layer through an etch process with a sulfuric acid/hydrogen peroxide type etchant. Therefore, the ultrathin copper layer is preferably uniform in thickness.
Herein, accuracy of the thickness of the electroplated copper foil strongly depends on the interelectrode distance between anode and cathode. A common method of forming an ultrathin copper layer involves formation of a release layer on a supportive copper foil (12 to 70 μm thick), on the surface of which an ultrathin copper foil layer (0.5 to 10.0 μm thick) and coarse particles by surface roughening are then formed. In the past the step after formation of the supportive copper foil uses the conveying system for the supportive copper foil in the form of zigzag path without a drum to support it as illustrated in FIG. 1. (Patent Literature 1)